1. Field of the Invention
The present invention relates to a printing head substrate, an ink jet printing head and an ink jet printing apparatus, and particularly, to a printing head substrate, an ink jet printing head and an ink jet printing apparatus, which are provided with a substrate temperature detecting element.
2. Description of the Related Art
An ink jet printing head mounted in an ink jet printing apparatus ejects ink droplets from ejection openings in various ways to attach the ink droplets onto a print medium such as a print paper, thus carrying out the printing. Among others, the ink jet printing head using heat as energy for ejecting ink can relatively easily realize a multi-nozzle system in high concentration, carrying out the printing with high resolution, of high image quality and at high speeds. There is known a so-called side shooter type of ink jet printing head as one of systems for ejecting ink using this kind of thermal energy, which ejects ink droplets perpendicularly on a surface on which heating resistive elements (heating elements) generating thermal energy are formed. In this type of printing head, ink supply at ink ejecting is generally carried out through ink supply openings penetrating through a substrate from a backside of the substrate provided with the heating resistive elements.
In the substrate of this side shooter type ink jet printing head, a plurality of heating resistive elements (hereinafter, also referred to as heaters simply) are provided at one side of the ink supply opening penetrating through the substrate centering the ink supply opening. Further, members are formed for forming ink ejection openings and ink flow passages for ejecting ink to correspond to the respective heating resistive elements. Such an ink jet printing head is formed of a monolithic configuration by a silicon semiconductor substrate based upon a semiconductor manufacture technology. Further, the ink jet printing head is provided with substrate temperature detecting elements because of a close relation between an ejection characteristic of ink droplets from the ejection opening and a substrate temperature.
FIG. 21 is a schematic diagram showing a construction of a conventional printing head substrate. There is, as shown in FIG. 21, known the conventional printing head substrate in which substrate temperature detecting elements 7 made of diode are arranged in the adjacency of input and output pads 12 and 13 (for example, refer to Japanese Patent Laid-Open No. 2004-050637). The substrate temperature detecting element 7 detects a temperature of the substrate, and a drive pulse is adjusted based upon the detected temperature information. This adjustment allows the printing without variations in image density even if a temperature difference occurs in the printing head substrate.
There is further known a printing head substrate on which substrate temperature detecting elements such as diode sensors are formed (for example, refer to Japanese Patent Laid-Open No. H2-258266 (1990)). It is possible to read a substrate temperature with high accuracy by forming the temperature sensor in the printing head substrate. This type of temperature sensor is used for controlling an ink ejection characteristic changing with heat generated at the time each power source consumes electric current. This type of temperature sensor is further used for forcibly and temporarily stopping the sequence by using a monitor value of the temperature sensor when an abnormality such as power source short occurs on the substrate to create an abnormal temperature increase.
In most of recent ink jet printing apparatuses, there is mainly used a printing head which has a plurality of ink supply openings within one substrate and a plurality of heaters are arranged in high concentration to correspond to the ink supply openings for obtaining an image with high resolution and of high image quality at high speeds. Since a high concentration arrangement of heater arrays is recently possible, the printing head substrate is, as shown in FIG. 21, configured to have one heater array to the one ink supply opening at one side thereof for downsizing the printing head substrate. Further, for achieving high-speed printing, the number of heaters per one heater array increases, and in consequence, there is a printing head substrate in which the heater arrangement array has a length of one inch or more. In such a substrate construction, the temperature detecting location is required to be a plurality of locations, such as locations not only near the pad as conventional but also in the adjacency of the central part in the heater array.
In the printing head substrate as shown in FIG. 21, however, in a case where an abnormal temperature increase occurs in the central part of the heater array 6, since a difference in the temperature distribution in the substrate occurs because of a distance from the central part of the heater array 6 until the temperature sensor 7 in the adjacency of the pad 12, a temperature in the central part of the heater array 6 may not be detected accurately. This problem is the more remarkable as the printing head substrate becomes the longer. Therefore, it is required to set the temperature sensor at a desired position for accurately detecting the temperature in the central part of the heater array.
FIG. 22 is a schematic diagram showing the construction of the printing head substrate in which the temperature detecting elements 7 are arranged near the central part of the heater array 6. In the substrate shown in FIG. 22, a logic circuit 15 such as a shift resister and a driver transistor 16 are arranged in such a manner as to be capable of reading out the temperature detecting sensors individually.
Even in the printing head substrate as constructed above, the substrate temperature detecting element made of diode has a large occupying area, and therefore, it is required to further provide a space for the temperature detecting element. That is, in a case of locating the temperature detecting element at the central part of the heater array, it leads to an increase in chip size, that is, substrate size.
In a case of detecting temperatures of the temperature sensors at plural locations, a logic circuit such as a shift resister is required for selecting a desired temperature sensor. In this case, it is preferable to locate the logic circuit near the temperature sensor in such a manner as to constitute one integral system. However, when the logic circuit is too close to the heater, it possibly causes instability in an operation thereof due to heat and therefore, it is required to locate the temperature sensor near the heater and locate the logic circuit at a position where it is not so much influenced by heat of the heater. However, when the temperature sensor is arranged in the center, the substrate size remarkably increases. In a case of the elongated substrate, a length of the printing substrate tends to be much larger than a lateral width thereof. Such a substrate of a large aspect ratio also possibly creates the problem with a mechanical strength of the substrate itself.